England number eight Billy Vunipola appears likely to miss at least part of the Six Nations after undergoing surgery on the knee injury he sustained against Argentina on Saturday.
The Saracens back row left the field during the first half of the 27-14 victory and had an operation on a torn cartilage on Sunday.
Vunipola is expected to be sidelined for a minimum of 12 weeks, ruling him out of next Saturday's clash with Australia at Twickenham and leaving him facing an uphill battle to be fit for the Six Nations opener against France on February 4.
"Billy's been absolutely fantastic for England over the last 11 months and we wish him a quick recovery," said England head coach Eddie Jones.
"He's a very influential player in the set-up and there's no doubt he'll be missed for the game against Australia.
"But where there is an injury there's an opportunity for someone else. We've had five or six frontline players missing throughout the series so I've no doubt we'll adapt and work that little bit harder this week.
"I'm sure the players will respond to this by going up a level and peak for this game."
Vunipola has started all but one game at number eight since Jones took charge following the 2015 Rugby World Cup.
He was one of three Saracens and England players - together with Maro Itoje and Owen Farrell - shortlisted for World Rugby's player of the year award, which was ultimately won by New Zealand fly-half Beauden Barrett.